[alphagrep12345]

Most conclusions from the comments seem to be that

1. Sourcing quality beans is costly. 2. Majority of the people don't care.

For 1 - For a single coffee shop, quality of beans is not the most significant part of price. They can increase ~10c per cup and get much better quality of coffee[0]. However, this might be tough as Starbucks need to source same beans across the world.

For 2 - Following 1, if you only need to increase 10c, and get significantly better coffee, why won't you do it? You're already the leader in 3rd spaces, why not be a leader in coffee too, for a much better moat?

[0] - https://www.youtube.com/watch?v=7SM2Jrot-ZM